Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$153.63	3.142%	$158.4571	$158.46	$158.45	$158.50
Purchase #2	$83.81	8.783%	$91.171	$91.17	$91.15	$91.20
Purchase #3	$44.35	13.767%	$50.4557	$50.46	$50.45	$50.50
Purchase #4	$118.89	4.563%	$124.315	$124.32	$124.30	$124.30
Purchase #5	$143.44	11.242%	$159.5655	$159.57	$159.55	$159.60
Purchase #6	$76.50	7.424%	$82.1794	$82.18	$82.20	$82.20
Purchase #7	$81.56	9.314%	$89.1565	$89.16	$89.15	$89.20
7 purchase totals =	$702.18		$755.3002	$755.32	$755.25	$755.50